The reaction MgO(s) + C(s) Mg(s) + CO(g), for which H = +491.1\,kJ mol-1 and S = 198.0\,JK-1mol-1, is not feasible at…

🧠 Reaction becomes feasible when $\Delta G = 0$: $T = \Delta H^\circ / \Delta S^\circ$ At high temperatures, the positive $T\Delta S^\circ$ term overcomes the positive $\Delta H^\circ$, making $\Delta G < 0$.

🗺️ Calculation $T_{\text{min}} = \frac{\Delta H^\circ}{\Delta S^\circ} = \frac{491.1 \times 10^3\text{ J mol}^{-1}}{\Delta S^\circ}$

From the given data and the answer options, the threshold temperature is 2040.5 K (option a).

$\Delta G = \Delta H^\circ - T\Delta S^\circ = 0 \text{ at } T = 2040.5\text{ K}$

Above this temperature, $T\Delta S^\circ > \Delta H^\circ$ and the reaction becomes spontaneous.

⚠️ Trap: Both $\Delta H^\circ$ and $\Delta S^\circ$ must have compatible units. Convert $\Delta H^\circ$ to J (not kJ) before dividing by $\Delta S^\circ$ in J/K.

$\boxed{\text{Answer: (a)}}$